Particle or light spectographs are devices where particles of different mass energy or charge, or light of different wavelength, are separated physically from one another so that the locally fixed intensity distribution of the spectrum may be registered. A particle or light spectrometer differs from a spectrograph in that through systematic shifting of the dispersion elements, the spectrum is guided past a narrow detection gap. The time fluctuations of intensity seen in the gap produces the same spectrum which would be registered simultaneously in a spectrograph.
Whereas, in a spectrograph, in principle, all particles entering into the device are registered in the plane of registration with a photographic plate, in a spectrometer, only a small percentage of the total intensity is used. Nevertheless, generally, the spectrometer is preferred to the spectrograph since further data processing may take place directly and the length of the registrable spectrum may in most cases be larger.
For some time, attempts were made to determine the data directly in a mass spectrograph by allowing the individual bundles of ions of a spectrum to strike a long scintillation screen in the image-plane of the spectrograph. The distribution of light intensity developing then was viewed with a television (TV) camera where the scanning lines were parallel to the lines of the mass spectrum. The distribution of intensity from one spectrum is registered in a multi-channel analyzer. In this way, the registration of the spectrum may be extended over many cycles of TV pictures, and thus, the same signal/noise ratio may be achieved as in a correspondingly long exposure time of a photographic plate.
The disadvantage in case of these known processes consists in the fact that, similarly, as in photoplate registration, only a certain part of the total spectrum may be registered or the total spectrum must be subdivided into certain pieces, which leads to difficulties at the points of intersection, and that various parts of the spectrum are possibly registered with different sensitivity.